This invention concerns a compensation device for chocks in four-high rolling mill stands with crossed displacement of the rolls.
The device is used to compensate for the crossover moment acting on the chocks of the back-up rolls and the working rolls as they cross over in four-high rolling mill stands.
The state of the art covers the rolling technique which includes the crossed displacement of the back-up rolls and/or working rolls (pair crossing) in order to obtain a better control of the profile of the rolled product during the processing step and therefore a final product of a better quality.
During the crossed displacement step, on the chocks of the back-up rolls, a moment of traversing is generated, caused by the misalignment of the forces of thrust which the rolled product imparts to the rolls with respect to the load exerted by the hydraulic pressure means and which act on the chocks of the back-up rolls.
This moment of traversing generates considerable friction between the chocks of the back-up rolls and the guide elements of the chocks, which are generally attached to the stationary uprights of the rolling mill stand, and this causes a greater rate of wear in the uprights and poor functioning in the whole rolling assembly.
This friction, and particularly that relating to the back-up roll situated on the side of the system to regulate the thickness of the rolled product (millscrews, capsules, etc.), considerably increases the mechanical hysteresis of the system which automatically regulates the thickness.
In these conditions, it is practically impossible to control the thickness and the profile of the rolled product with precision, and therefore the products obtained are not of optimum quality.
The Applicant is not aware of any experiments in the prior art which have tried to solve this problem or proposed solutions thereto.
As described in for example EP-A-0.707.902 and JP 60-099405, the use of thrust or lifting means which act on the side faces of the supporting chocks of the rolling rolls has been known for some time; however the function of these means has always been either to impress a desired camber lengthwise to the roll, or to absorb the curving reaction of the roll caused by the rolling passes.
For this reason, the prior art has never thought of correlating the push-and-pull action on the ends of the rolls to the actual crossover position of the rolls with respect to the rolling axis or to the misalignment with respect to the median plane of the rolling mill stand.